Electrodeposition of copper powder



June 9,, 1942.

s. B. TU WINER ETAL ELECTRODEPOSITION OF COPPER POWDER Filed Feb. 4, 1938 2 Sheets-Sheet l mj w m WmA m June 9, 1942. s. uw ETAL 2,285,762.

ELECTRODEPOSITION OF COPPER POWDER Filed Feb. 4, 1938 2 Sheets-Sheet 2 Il'rwwbow- I Emma 35.3mm "mvwemnmomm 5,5 f mam Patented June 9, 1942 UNITED STATES PATENT OFFICE I ELECTRODEPOSITION OF COPPER POWDER Sidney B. Tuwiner, Kew Gardens, andWilliam H. Osborn, New York, N. Y., assignors to Phelps Dodge Corporation, New York, N. Y., a corporation of New York Application February 4, 1938, Serial No. 188,770

12 Claims.

This invention relates to the preparation of copper and particularly tothe electrodeposition of copper in flake form.

Copper powder is used as a pigment ingredient in the most durable types of paint for the coating of steel and wood in manufacturing plant maintenance, for antifouling paints, under-water ship hull paints and for other marine paints. Such paints, including air-drying varnish vehicles, have the property of retaining a certain degree of plasticity or life, thereby resisting the embrittling effect of prolonged weathering, which causes many other types of paint to fail by checking, cracking and flaking. Copper paints have been shown to be excellent for prime coats as well as for overcoats for metal painting.

Copper is also sometimes present in paints as .one of the constituents of a flake material referred to in the trade as "bronze powders. Socalled gold" paint, for example, is a bronze powder made from an aluminum-copper alloy' Other metal pigments having a golden. lustre. containing copper are made in colors from bronze to that of copper. Even the so-called copperbronze paints, however, are made from copper alloyed with other metals, principally zinc. The pigment powders for all these copper alloy paints, in common with aluminum powders, have been made in the past by the pounding of the alloy into the form of very fine flakes.

densities and unusually low acid and copper concentrations in the electrolyte.

An object of the present invention is to provide a process whereby pure copper may be electrolytically deposited in flake form. vA 'further object is to provide means and a method for controlling the conditions in the electrolytic cell so that the copper will be deposited in flake form. Another object is to provide such a process by which the flake copper so deposited will be coated with an oily or greasy film.

It is also an object'to providea process for producing. copper in flake-like form under the normal conditions of electrolyte composition, temperature and current denzity used in tank room cooper refining, and. thereby to perform the operations of refining the copper and reducing it to flake form in a single step with very little additional cost of power and labor over that required for the production of ordinary cathode copper.

It is another object to produce a new product and a new procedure useful in the preparation of copper paints and other copper-containing products. Other objects ,will become apparent.

It has now been found that by electrolytically depositing copper upon a cathode in an electrolytic cell, which cathode isooated with a particular type offilm, the copper so depositedwill be in the form of an aggregate made up of individual flake-like or laminar particles instead of the usual tree-like particles and that such particles will be coated with a coating re-' sulting from the film used. The selection of the film and the control of the oxidizing properties of the electrolyte during the electrodeposition are important in obtaining the desired results.

.It has been found, for example, that a vegetable oil (or other glyceride oil or the fattyacid, or other derivative containing the fatty acid radical, corresponding to the glyceride of the oil) containing a saturated or an unsaturated hydrocarbon chain together with one or more hydroxyl groups, and having a certain degree of oxidation, may be used to form the film on the oathode'. The coating applied may be one that alreadyhas the required degree of oxidation or the required degree of oxidation may be obtained by controlling the oxygen content of the electrolyte. Important characteristics ,of the present preferred materials forming the film on the cathode during the 'electrodeposition are first, that they contain fatty oils, fatty acids or derivativesof these containing the fatty acid radical, or mixtures of two or more of these, in which there is present in the free or combined fatty acid radical, one or more hydroxyl groups, and secondly, that there must be present in the oil a definite degree of oxidation, perhaps accom-v paniedby the formation of peroxide groups in the fatty acid radical. The coating on the oathode may also contain other substances, such'as lubricating agents, or other agents useful in preparing, or for modifying the character of, the

finished powder. Such other substances should be present in suflicient quantities to give the desired effect, but in insuflicient quantities to deleteriously affect the electrodeposition of the flake copper.

Castor oil or the fatty'acids from it are the pared as hereinafter indicated, or otherwise.

may be used or that fatty acids or fatty acid glycerides or other glycerides containing the desired hydroxyl groups may be synthesized or pre- The oxidation of the coating material may be effected in a number of ways, for example:

1. By chemical oxidation, as by mixing the coating material with an oxidizing agent, such, for example, as a solution of hydrogen peroxide, sodium peroxide, potassium permanganate, etc. or perchloric acid or concentrated sulfuric acid, etc.

2. By blowing the coating material, before its application to the cathode, with air or other oxygen bearing or oxidizing gases or by applying the coating material to the cathode, in the form of a fine spray or by otherwise contacting it with an .oxidizing gas; such oxidation is somewhat accelerated by elevated temperatures.

3. By the absorption of the coating material during the period of electrodeposition, of oxygen dissolvedin or carried by the electrolyte.

The hydroxyl group may be obtained, for instance:

1.. By using castor oil or mixtures of castoroil and/or its fatty acids or other natural glycerides containing at least one hydroxyl group.

2. By the hydrolysis of the peroxide or other oxidized groups formed -.by one of the above methods of oxidation. This hydrolysis results, for example, from the reaction of a fatty oil or other glyceride or fatty acid, having unsaturated bonds, with an acid copper sulfate solution. For instance, the hydroxyl groups may be formed in situ by the reaction between an oil or fatty acid having a high iodine number, such as a linseed oil that has been boiled with a metallic drier,

with the acid copper sulfate electrolyte. This reaction goes rapidly at'temperatures above 150 3 J F. and at an appreciable rate at lower temperatures. The formation of hydroxyl groups in this way is accompanied by the "destruction of some or all of the peroxide or other oxidized groups, so further oxidation may be necessary.

Thus, the control of the electr'odeposition to obtain the desired result may be eflected by regulating the degree of oxidation of the coating or film on which the copper deposit is to be formed. This may be accomplished by saturating the electrolyte with oxygen, for example, by splashing it into the tank, by spraying it, by dispersing or passing oxygen or an oxygen carry: ing gas to or through it, or by circulating. it through a depositing out cell containing an insoluble anode or by other suitable means. When the'control is affected in this way, the coating film on the cathode need not be preoxidized before the cathode is put in the electrolyte.

Or the control of the oxidation of the coating or film may be accomplished by subjecting the coating or film to a regulated pre-oxidation, either by the useof oxidizing chemicals or by exposing it to contact with oxygen or oxygen carrying or other oxidizing gases, in which event the oxidation of the electrolyte may be controlled or minimized by'exclu'ding oxygen from it and avoiding excessive splashing of the electrolyte.

Of course, regulated combinations of these two 75 -of Figure 3).

methods for effecting control of the oxidation of the coating material or film may be utilized. For example, the coating material or film may be preliminarily chemically or otherwise treated to increase its susceptibility to oxidation, after which it may be subjected to a less intensive oxidation, either in the electrolyte or before, to obtain the desired result.

The temperature of the electrolyte may also be regulated to control the effectiveness of the oxidation of the coating. material or film in the electrodeposition. For example, where there is excessive oxidation of the coating material or film, through the electrolyte or otherwise, this excessive oxidation may be compensated for to a certain extent by raising the temperature during the electrodeposition. V

In describing the invention, reference will be made to an apparatus suitable for use in carrying it out, although it is not intended to limit the invention to the particular apparatus or details of procedure referred to in the description. .-Figure l is a diagrammatic side elevation of an apparatus suitable for carrying out the proc- Figure 2 is an enlarged plan view of the electrolyte tank shown in Figure'l.

Figures 3- to 8 are photomicrographs of copper deposited in accordance with the invention.

Figure 3 is of a sectional fracture of the deposit stripped from the cathode blank, the side of the specimen at the left having been in contact with the cathode blank. Figure 4 is of the outer surface of the deposit (the right hand side Both of these views were taken with vertical illumination at a magnification of '32 diameters.

Figure 5 is of powder settled dry on aglass snde with, vertical illumination. Figure 6 is of particles of the powder imhedded in a resin' Figure 8 is of .particles of the powder settled 1 dry on a glass slide. It is taken with dark field illumination at a magnification of 1000 diameters.

Referring to the drawings of the apparatus, the numeral l indicates an electrolytic cell having a wooden frame 2 and a lead lining 3. On the top of thistank is placed a wooden frame 4 for supporting two triangular contact bars .5 and 5a. The anode supporting bars 8 contact the triangular bar So at one end'and rest upon the wooden frame I at the other end; The cathode blank carrying bars I rest upon the triangular bar 5 at one end and upon the other side of the wooden frame l at the other end.

The cathode blanks are made of sheet copper, 3 which may be riveted to the supporting bars I.

The anodes used are regular cast copper anodes. The anodes may be supported by means of copper rings to under lugs on-the anodes .and over the copper bars 6, which support themand provide electrical contact with the anode contact bar 5a. If desired, the cathode and anode supporting ,bars may be constructed and arranged so that all of the cathodes and/or all of the anodes may be immersed in and withdrawn from the cell simultaneously by means of a suitable rack and lifting cranes.

' lyte.

type of spray gun.

The electrolyte may'be circulated through an external circuit to maintain it uniform and at the desired temperature which may be about 125 to 140 F. and preferably about 130? F. This external circuit may include a depositing out cell or other means for regulating the-oxygen slimes, whereby the electrolyte above the slime level may be withdrawn and the slimes may be washed by means of water into a suitable receptacle. Also, if preferred, the electrolyte may be fed in near the top of tank I and withdrawn from near the bottom of that tank.

The electrolyte in'the sump tank l may be pumped to a head tank I I by means of a centrifugal pump l2 suitable for handling the acid copper sulfate electrolyte, or by other suitable means, such, for example, as an air lift pump.- The' head tank Il may be provided with a heating element I3, heated by steam or electricity or other suitable means, with thermostatic control for regulating the temperature. The tank Il may be provided with a discharge pipe l4 connected with the pipe 8 through a gooseneck l5, so that liquid can never be discharged below a definite point in the tank II, in order to protect the heater l3- from exposure in the event an electric heater is used. Of course, when other means is provided for heating the liquid,

it may be desirable to eliminate this feature. An open vent Ia is provided in the gooseneck l5 and an overflow pipe Ila, leading back to the sump tank I0, is provided so that a constant head may be maintained in the head tank II by circulating an excess of liquid with the pump l2.

If desired, either or both of the sump tank I0 and the head tank ll may be provided with cathode blanks and lead sheet anodes, of the same size, for the purpose of depositing out the copper that tends to build up in the electro- The oxygen liberatedat the lead anodes in such. an arrangement also serves to aerate the solution flowing to the electrolytic tank.

As a specific example of the carrying out of our invention in an apparatus as described above, the cathode blanks may be sprayed with hot oxidized castor oil by means of an atomizing The oxidized oil vmay be prepared by stirring about 1% by weight of perchloric acid (about 60% perchloric acid in aqueous solution) into a good clear grade of raw castor oil (AA grade) in a kettle heated, for instance, to approximately 212 F. by steam, or

other suitable means, toreduce its viscosity.

The hot oil may be drawn from this kettle and sprayed as it is required. Or the cathode blanks may be dipped in the hot oil. I

The oxidized oil, heated to a lower temperature if desired, may be thinned with a mixture of commercial grade'denatured alcohol and enough carbon tetrachloride may be added to remove the fire hazard. The cathode blanks may then be sprayed with or dipped in this mixture and the solvents evaporated.

The degree of oxidation of the oil applied depends to a certain extent upon the temperature and the fineness of division of the particles. If the oil is sprayed with a non-atomizing type of spraygun, or if the cathode is dipped, a lesser amount of oxidation of the coating will occur than when the oilis atomized. Similarly, if the temperature is reduced, the degree of oxidation will be decreased. Variations in the degree of oxidation maybe compensated for byreducing or increasing the quantity of perchloric acid used or the amount of oxygen in the electrolyte or the temperature of the electrolyte.

The cathodes prepared as described above may be placed in the electrolytic cell l, spaced, for example, at about 41/ inches and with the anodes equally spaced between them.

A constant condition of aeration may be maintained by circulating the electrolyte, the electrolyte being, in effect, partially saturated with oxygen by allowing it to splash or by other means mechanically bringing it into contact with air.

The electrolyte may be brought up to the proper temperature (preferably no higher than F. nor lower than 120 F., although satisfactory results have been .obtained at higher and lower temperatures). Current may be supplied to the anodes so as to give a current density of about 15 amperes per square foot of anode surface, the corresponding cathode current density being about 15 amperes per foot. Satisfactory results may be obtained with a greater or less current density, but it is preferred to use an anode current density of about 15 to 20 amperes per square foot and a cathode current density of about 15-20 amperes per square .foot.

Concentrations of copper sulfate, sulfuric acid and electrolyte impurities need be no different from the usual tank room electrolyte for electrodeposition of copper. It is advisable to maintain a chloride content of about .001 to '.003% by addition of chloride compounds, for

example, sodium chloride or hydrochloric acid.

With a cathode sprayed with an oxidized oil as described above, the dissolved oxygen in the tank electrolyte should be the equivalent of that present in. an electrolyte through which oxygen has been bubbled to such an extent that bubbles of essentially pure oxygen will appear when ,a sample of the electrolyte is heated to F.

The system.may be maintained constant by regulating the temperature and circulation of copper in the form of fine laminae or flakes is produced.

Figures .3 to 8 illustrate the form of the deposit. The sectional fracture enlarged in Figure 3 illustrates the honeycomb structure of the large number of fine flakes and shows that the flakes intersect at angles of approximately 60. Figure 4,1ooking at the surface of 'such a deposit, indicates that the multiplicity of these planes intersect to form tetrahedronal pyramids,

each with its apex pointing outward from the cathode blank. Figures 5, 6 and 7 further illustrate the laminar or flake-like structure. Figure 5 is a photomicrograph of the powder obtained directly from the electrolytic deposit, without further treatment, except drying. In Figures 6 and 7, which are of such a powder'susillustrates the fine structure of a typical flake of the electrolytic flake copper powder. Its structure consists of three sets of lines intersecting one another at angles of 60 and shows that the deposited flakes have a well defined crystalline structure. The faces of the copper flakes are sections of the (111) planes of crystalline copper. (The plane passing through the outer terminals of the three edges of a unit cube converging at a single corner of the cube, or planes parallel thereto, are 111 planes.)

This product has many uses and is particularly suited for the production of copper paints, inks, etc. The oil on the cathode blank supplies a coating of oil around the flakes of copper which expedites the subsequent wetting of the particles with the oil vehicle of the paint.

Instead of depending upon splashing or spraying to dissolve oxygen in the electrolyte or oxidize the coating composition, pure oxygen may be bubbled through the electrolyte or the coating material. Or the castor oil or other oil or substance containing the hydroxyl group maybe reacted with neutral potassium permanganate, followed by washing with hydrochloric acid to discharge pipes. This run lasted for 68 hours.

Good results have also been obtained by sprayingthe cathode with mixtures of castor oil and linseed oil. For example, excellent deposits were.

obtained with a mixture of 75% linseed oil and 25% castor oil, slight aeration being maintained by allowing the discharge liquor fromthe pump to splash upon the surface of the electrolyte in the head tank. The temperatures were maintained at about 128 to 143 F. With moderate aeration excellent powder was obtained with such a mixture at temperatures of 133 to 137 F. The.

temperature of spraying the oil onto the cathode was varied from 100 to' 180 C. without observable difference.

decompose the manganese dioxide. Or hydrogen peroxide may be used to oxidize the oil. The.

Good flakes were alsoobtained using castor oil treated with .5 to 2.5% of perchloric acid (60%). The perchloric acid was stirred into the castor oil (grade AA) until an emulsion was formed at room temperature. The emulsion was then heated to 90 to 100 C. until it was changed to a clear, slightly brown colored solution, which was sprayed onto the cathode. The temperature was maintained at 126 to 130 F. and electrolyte aeration was minimized. In these tests very good flake deposits were obtained in runs lasting for 22 to 4'7 hours.

Good results were also obtained by treating the castor oil to be applied. to the cathode with perchloric acid (60%) or sulfuric acid (95%) as hereinbefore described, and controlling the oxidation of the electrolyte by passing gaseous oxygen through the electrolyte in the head tank, the

' said gaseous oxygen being difiused through a The treatment of castor oil with sulfuric acid results in a mixture of sulfated or sulfonated produced separately and added to the castor oil, or Turkey red oil, which is a sulfated castor oil neutralized to destroy excess acid, may be added to the castor oil. The desired percentage of sulfonated or sulfated castor oil, or Turkey red oil, varies with the oxygen content of the electrolyte and with the degree of oxidation of the castoroil. The greater the oxygen content or degree of oxidation of the castor oil, the smaller is the quantity of sulfonated castor oil or Turkey red oil that should be used in the mixture. Satisfactory results may be obtained in the electrodeposition described above when a castor oil treated with 1% of sulfuric acid is sprayed with an atomizing spray gun onto the cathode blank and the oxygen content of the electrolyte is equal to that of an electrolyte in which bubbles of pure oxygen would start to be liberated at a temperature of about 190 F.

Satisfactory results have been obtained using about 4 /2 to 5% by weight of sulfated castor oil or Turkey red oil in castor oil, with electrolyte temperatures of about 122 to 157 F. and circulating with an air lift pump whereby a condition of intensive electrolytic aeration was obtained.

Good results have also been obtained by saponifying castor oil with 25% of sodium peroxide and a minimum of water, the mixture being heated to 212 F, and cooled and acidified. This oil was diluted with 5 times its weight of raw grade AA castor oil and sprayed on the cathode. The electrolyte temperature was maintained at porous thimble in the bottom of the tank. The oxygen content of the electrolyte was measured by heating a-portiori of the electrolyte very gradually and noting the temperature at which bubbles of essentially pure oxygen appeared.

Good depositswere obtained by following this procedure and using percentages of sulfuric acid from about 2.5 to 1% at electrodepositing temperatures of about 124'to 131 F., the oxygen content being such that bubbles of oxygen appeared in portions of the electrolyte that were heated to about to 192 F. A fair deposit was obtained with .1% sulfuric acid at an electrolyte temperature of about 128 F. and-with oxygen bubbles appearing at about 184? F. 1

Similar results were obtained with castor oils tieated with perchloric acid (60%) amounts given above and at the same range of electrolyte temperatures, the oxygen content of the electrolyte being such that the bubbles of oxygen appeared on heating the electrolyte at the same range of temperatures. Oxidation with perchloric acid appeared to give better results than the oxidation with sulfuric acid, inasmuch as the deposits were more uniform and the flakes were finer. Also, it was less sensitive to changes tures the viscosity of the oil is reduced to a point at which it tends to rise along the blank, becoming thin at the bottom and heavier at the top,

in the I Also, if the wetting power is too great, the crystal so that the deposit is of an uneven character. Satisfactory results were also obtained with temperatures outside of this range for a portion of the electrodeposition period. It was found desirable to maintain the chlorine content of the electrolyte at about .001%. This may be accomplished by adding hydrochloric acid or salt, etc.

Electrolytes that analyzed 14 to 20% free H2804, 2.4 to 4% copper and .001% to .004% of chlorine have been found to be satisfactory. It

is preferred to maintain the electrolyte within the range 6 to 18% free H2804, 3'to 3.5% Cu and .0015 to .003% C1.

Satisfactory deposits have also been obtained with boiled linseed oil containing a lead drier and with mixtures of Turkey red oil with various fatty acids.

From a practical consideration it is desirable to operate. so as to obtain a satisfactory deposit for the longest possible period. As the length of the run increases the percentage of coarse flakes decreases. Generally speaking, when the product is required to be such that after the initial disintegration and flotation 85 to 90% of the metal will pass through an 80 mesh sieve, the run should be limited to about 24 hours. This Period may be lengthened by more accurate control of the conditions in the cell during the electrodeposition. If there is a larger measurev of tolerance the run may be extended up to 72 hours or more. To lengthen the run the oxygen contained in the electrolyte or the degree of oxidation of the oil or the susceptibility of the oil to oxidation should be slightly decreased. Too much oxidation tends to shorten the period before the deposit becomes tough and flakes are no longer deposited. On the other hand, too little oxygen tends to cause the initial deposit formed to be coarse and possibly tough; but after a time the flakes deposited will become finer and better. In order to avoid coarse particles in the powder, it is desirable to keep this induction period as short as possible.

Although it is not intended to limit the invention to any particular theory of operation, it is believed that the oil or other coating material accomplishes its function by stopping or strongly retarding the component of crystal growth in either direction perpendicular to one of the (111) g planes and to allow growth to proceed in the (111) plane. Thus the growth may proceed freely along the face of the plane but to only a restricted degree along a perpendicular to th: plane. The function of the oil or other coating is to selectively wet the deposited copper so as to limit the component of its growth perpendicular to the (111) plane.

Thus by wetting the (111) planes of the copper crystal lattice far -moreefiectively than any other plane, the component of growth pe p ndicular to this plane is inhibited while the growth is permitted to proceed parallel to or a laminar crystal.

Three factors are along this plane, resulting in important intheir effect upon the orientation of the molecules of oil other coating material: (1) the attraction (wet-"- ting) holding one part of the molecule to the face ofa copper crystal; (2) the effect of the electric fidd, which is perpendicular to the cathode surface; and (3) the orientingeffect of the attractive and repellent forces of neighboring molecules. The first of these must'be present if the 011 is to wet the copper at all, which apparently is 'essential to the formation of flake deposits.

growth may be hindered parallel to as well as of wettingis determined, in the case of fatty acids and their glycerides, by the degree of oxidation imparted or obtained.

The second factor is responsible for the orientation of the flakes symmetrically about lines perpendicular to the cathode (see Figure 3).

The third factor affects the nature and sizes of the individual flakes. If the oil molecules on the surface of the copper are strongly attracted or associated, and if their configuration is such that they may properly align themselves, they will tend to be well oriented and the laminar crystals will grow in area very considerably before interruption occurs, leading to crystallization in another of the four possible directions. When-the interruptions are relatively few, the individual flakes grow quite large and the deposit is very bulky. On the other hand, when they are numerous, the individual flakes are smaller and the deposit more compact. Hydroxyl and peroxide groups favor association and hence this type of molecular orientation. For the best molecular orientation it is' desirable that the molecules have essentially a chain structure.

Although we have given a number of specific examples of. coating materials suitable for accomplishing the desired result, it is not intended to limit the invention to these, since it will be apparent that other substances that will selectively inhibit or retard the growth of the crystals in various directions, may be used in place of the illustrative examples.

The aggregate of flakes stripped from the cathodes in following the above described procedures may be washed by means of any suitable washing device. The washings may be returned to the tank electrolyte, if desired. For instance, the flakes may be covered with water and allowed to soak for a day, after which the supernatant liquor may be returned as make-up water to the sump tank. The remaining flakes may be dumped into the agitator in which it may be allowed to remain until the time at which it is desired to operate the flotation cell.

The contents of the agitator-may be agitated by an impeller, which serves to disintegrate the agglomerated lumps of flakes of copper, and discharged into the flotation cell. The flotation cell may be of the usual type provided with an impeller. It is preferred to use a cell of the subaeration type; i. e., one with an impeller and an air inlet under the impeller. The oil films on the particles of copper, resulting from the oil applied to the cathode blank, provides a flotation agent so the flotation cell 'may be operated without any reagents other than the oil already present on the copper flakes.

If desired, the disintegration and flotation may both be accomplished in the flotation cell by providing a suitable 1m eller therein.

A classification of the particles is achieved in the flotation cell, the coarse lumps being allowed to 'collect'in the bottom of the machine. The fine froth may be discharged by means of a scraper and may be de-watered in a centrifuge or other suitable water separating device, such, for ex-- ample, as a continuous rotary filter. Hot water may be used in washing the flakes during this operation. l v

The cake from the'centrifuge or rotary filter contains approximately 20% water which may be removed in a drier, operated at a temperature of not higher than 550 F. The atmosphere in the drier should be inert, containing such gases as carbon dioxide, nitrogen, etc. Where a -rotary kiln type of drier is used, a continuous rotary filter may be used, while if a batch drier is used, a centrifugal separator may be preferable. The drying may be suitably accomplished by heating with steam heat while applying a suction. In order to avoid the possibility of oxidation, the air in the drier may be displaced with carbon dioxide or other inert gas before the application 'of heat and vacuum and the inert gas may also be allowed to bleed into the drier during the first few hours of the drying operation. After the drying, cooling water may be passed through the heating unit to cool the flakes and after cooling the vacuum may be broken and the flakes removed.

The material discharged from the drier may be disintegrated in a ball mill, etc., to prepare it. for use in the production of paints, inks, etc. or t for other desired uses. In such preparation, it is preferred to avoid oxidation of the copper powder and the disintegration is preferably carried out in the absence of oxygen by displacing the air in the mill with carbon dioxide or some other inert gas before the grinding. Also, in the preparation of flake copper for use in paints, etc.. it may be desirable to avoid leafing or mirroring of the flakes. Such leafing or mirroring cause the particles of copper to float to the surface of the paint, etc. vehicle and remain there after drying of the film, with the result that the copper is exposed to the atmosphere and will tarnish easily. For some uses it is preferred to prepare the flakes in such a manner that it will be completely dispersed and distributed throughout the 7 body of the film, so that the particles will be protected from the atmosphere.

Various solvents, vehicles, resins, etc., useful in the preparation of paints, etc., may be added to the copper flakes before or after the disintegration of the dried product. It is desirable that the vehicle used be quick setting in order that the coagulation or settling of the metal flakes during the period of drying will be avoided. A good dispersion of the pigmentis relied upon to obtain the desired high covering power and dispersity. An example of a vehicle which meets the requirements specified above is a short or medium oil alkyd resin containing about 35% of the film formingingredient in solution in a toluolxylol thinner and having a viscosity of 2 to 2 /2 poises. The relatively high viscosity serves to aid the dispersion of the flakes and to avoid leafing. An example of an entirely different type of vehicle, equally successful, is a varnish made from Tornesit (a chlorinated rubber compound), plasticized with Arochlor (a chlorinated biphenyl),

which may be dissolved in a mixture of xylol andhydrogenated petroleum thinner. The number of other materials which may be used is large.

The percentages referred to in this application are by weight. 7

It is obvious that many variations may be made in the procedures described for depositing the aggregate and for preparing it for various uses and it is not intended to limit the invention to the particular examples and ilustrations given.

position containing an oxidized fatty acid radical having a least one hydroxyl group.

2. A method for preparing metallic copper in fine flake form comprising electrodepositing copper, from an aqueous acid solution of a copper compound, upon a cathode carrying a composition containing an oxidized fatty acid oil having at least one hydroxyl group in the fatty acid radical. f

3. A method for preparing metallic copper in fine flake form comprising electrodepositing copper, from an aqueous acid solution of a copper compound, upon a cathode coated with a composition containing an oxidized castor oil.

4. A method for preparing metallic copper in fine flake form comprising electrodepositing copper from an aqueous acid solution of a copper salt upon a cathode carrying a composition that is a flotation collecting agent and that contains an oxidized fatty acid radical having at least one hydroxyl group, stripping the copper from the cathode, churning it into a fine froth and separating the fraction containing the fine particles.

5. A method for preparing metallic copper in fine flake form comprising electrodepositing copper, from an aqueous acid solution of a coppercompound, upon a cathode carrying a composition that is a flotation collecting agent and that contains an oxidized fatty acid radical having at least one hydroxyl group, stripping the copper from the cathode, washing it, churning it into a fine froth, separating the fraction containing the fine particles and drying the fine particles in an inert atmosphere.

, 6. A method for preparing copper in fine flake form, which comprises electrolytically depositing the copper from an aqueous acid solution of a copper salt upon a cathode face coated with a The terms used in describing the invention have been used in their descriptive sense and not as terms of limitation and it is intended that all equivalents thereof be included within the scope of the appended claims. j

composition containing an oxidized fatty acid radical having at least one hydroxyl group, which causes the deposition of an aggregate of laminar crystals and coats these crystals with a flotation collecting agent, stripping the aggregate of crystals from the cathode face, churning the mass into a fine froth wherein the said coating material serves as a flotation collecting agent, and separating the fraction containing the fine particles by froth flotation.

7. A method for preparing flake copper, comprising electrodepositing copper from an aqueous acid solution of a copper salt upon a cathode carrying a composition containing an oxidized fatty acid radical having at least one hydroxyl group, stripping the copper from the cathode, washing it free of electrolyte, and drying it at a high temperature. v Q

8. An article of manufacture comprising a pure metallic copper .electrodeposited in flake form and having thereon a film of an oily composition containing an. oxdized fatty acid radical having at least one hydroxyl -group, said flake copper being electrodeposited from a cathode coated with said oily composition.

9. An article of manufacture comprising electrodeposited flakes of copper, the faces of which correspond to (111) planesbf the crystal lattice, said flakes being coated with an oily or greasy material-containing an oxidized fatty acid radical having at least one hydroxyl swap and upon a cathode carrying a composition contain fine flake form, comprising electrodepositing' copper from an aqueous acid solution of a copper compound, at temperatures of 120 to 140 F.,

ing an oxidized fatty acid radical having at least. one hydroxyl group.

12. A method of preparing metallic copper in fine flake form, comprising electrodepositing copper from an aqueous acid solution of a copper compound, at temperatures of 120 to 140 F, and current densities of 15 to 20 amperes per square foot, upon a cathode carrying a composition containing an oxidized fatty acid radical having at least one hydroxyl group.

SIDNEY B. TUWINER. WILLIAM H. OSBORN. 

